Frozen master cylinder piston!!

[AG GL]

Help!!
How can I get it out to replace with new? I've had it soaking for over a week now in WD 40 and have tried to blow it out with air. Nothing!

AG GL

[Matchless]

OK, does it move at all if you push it in? Have you removed the circlip?

Once the circlip is out and the piston moves in when pushed carefully, scrape as much of the grunge away without damaging the metal. Now use a blunt screwdriver to push the piston in and release it sharply so that the inner spring pushes the piston back like firing a gun. Do this a few times and it should pop out. I usually slip it off into the handle opening
If it is locked solid, drill a hole in it and try to turn a large self tapper into the hole, if the piston starts turning you may be in luck and be able to pull it out with the self tapper.
Otherwise the corrosion may already have damaged the bore and you will need a new one or have it re-sleeved.
Good luck.

[Ironriot]

Help!!
How can I get it out to replace with new? I've had it soaking for over a week now in WD 40 and have tried to blow it out with air. Nothing!

AG GL

WD40 isn't meant to be a penatrant. Try soaking it in PB Blaster

[duaneage]

I would replace it. Brakes are rather important.

[cloudbreakmd]

I have to agree with replacing the part. Although you may fix it temporarily, brakes are as good as having good tires in my book.

[retrex]

Piston out

1st thing is that the gunk in and around your master is dried brake fluid, wd dosen't do anything to desolve or pentrate it. Use denatured alcohol or xylene. If it is a front master then after you have removed all the mechanicall retaining hardware and have soaked it in the right solutions you have a couple of ways of removing the piston with increasing levels of damage. The first method I try is the slam it down on the workbench method. With the master firmly in hand, the master open end down, with increasing levels of force slam it onto the workbench surface. I put something on the bench that is soft enough to keep the master from denting or breaking. Be careful not to lift it from the bench to quickly after the impact as the piston is spring loaded and will fly off into the nether regions of your shop. If this doesn't work I go to the vise and needle nose method. Put the master in a vise and take a pair of long needle nose pliers and grab onto the piston post end, the part that the lever pushes against, and give it a good tug and sometimes you get lucky. Try not to grab onto more than one spot on the post as this method does damage it a bit. The next thing I try is the tap the post end and leverage it out. With this method the piston needs to be replaced. Drill a hole in the post end, try to center it, and screw int a 3 inch sheet rock or deck screw. Make sure you get a good bite into the post. Place the master in a vise, place a block of wood on the master to lever against, put a claw hammer on the screw head and try and lever the piston out. Just like trying to remove a nail from wood. Sometimes you get luckly, sometimes you don't. If you master isn't working what have you got to lose.

good luck

[dardoonk]

If it is the front master cyl, then just replace it with something from a newer bike. Pretty much anything that has a 7/8" bar will work. I used a Kawi ZX-14

You can get them on ebay for not much more than what it costs to rebuild your stocker, and you end up with a better product with less time invested..

http://cgi.ebay.com/ebaymotors/FRONT...QQcmdZViewItem

[Matchless]

If it is the front master cyl, then just replace it with something from a newer bike. Pretty much anything that has a 7/8" bar will work. I used a Kawi ZX-14

The Master Cylinder inner diameter is quite important. Most smaller bikes use 1/2" and most larger bikes or double disks use 5/8". It is usually stamped somewhere on the underside of the M/C.
A 5/8" on a smaller bike (that is designed for 1/2") will give a very short hard pull on the brake handle before stopping and a 1/2" on a bike designed for a 5/8" will give a longer softer pull, sometimes right close to the grip before brakes take fully.
The more pistons or larger pistons on the wheel side, the larger the volume of fluid that needs to be moved.

[dardoonk]

The Master Cylinder inner diameter is quite important. Most smaller bikes use 1/2" and most larger bikes or double disks use 5/8". It is usually stamped somewhere on the underside of the M/C.
A 5/8" on a smaller bike (that is designed for 1/2") will give a very short hard pull on the brake handle before stopping and a 1/2" on a bike designed for a 5/8" will give a longer softer pull, sometimes right close to the grip before brakes take fully.
The more pistons or larger pistons on the wheel side, the larger the volume of fluid that needs to be moved.

Good point. As a matter of how it will feel, there definately will be a difference. For each 1.0mm of movement, a 5/8" m/c will move 49.85g/mm of fluid. A 1/2" m/c will move 39.89g/mm fluid. (not movement of the lever, this is the movement of the m/c piston). With less fluid to move, the 1/2" piston feels more firm sooner, while the 5/8" piston moves more fluid before it reaches the same "firmness", so to speak.

I don't know if AG GL is running 1 or 2 calipers, or even what year bike, so it's impossible to calulate how much the brake pads move for each 1mm of m/c movement. Assuming he's running stock calipers and hasn't adapted a set of 4 or 6 pots, both masters will move enough fluid to stop the bike.

If he's got brakes that have a larger number of pistons, a m/c could run out of travel before the pads move far enough. Obviously, this would occur sooner using a 1/2" m/c, so larger bikes or multi-pot brake systems would generally have the 5/8" m/c.

[AG GL]

I thank you all for the suggestions offered to help free up my M/C piston.
I should have posted this sooner. I did get the piston removed ok after simply driving it into the cylinder a bit, then removing with the needle nose pliers. It went well after realizing that they don't typically 'freeze up' in the compressed position. Cleaned up nicely and now overhauled.
I've also overhauled the calipers during this time. Now waiting for some SS lines to arrive and then I'll have front brakes...

Thanks again!

AG GL

BTW-Its a GS 850 G...